A color liquid crystal panel is utilized over a wide field in display devices of information instruments, etc., and with the progress of the recent information-oriented society, the development aiming at a larger picture and a higher precision has been made.
In such a color liquid crystal panel, to increase the contrast of the picture and to sharpen the displayed picture by increasing the coloring effect, each black matrix showing a less reflectance and having a good light-shielding property is disposed between each color filter pixels of red (R), green (G), and blue (B).
Hitherto, the black matrix is produced by applying patterning by etching using a known photolithographic technique to a low-reflective thin-film substrate formed by laminating metal layers, etc., by sputtering metal targets such as chromium, etc. As such a laminated low-reflective thin-film substrate, a low-reflective thin-film substrate formed by laminating a chromium oxide layer and a chromium metal layer is known.
In this case, because the reflectivity is restrained by the interference of light by the laminated layers in multilayer and the laminated layers included a chromium metal layer having a high reflectivity and a less transmissibility of light, the laminated low-reflective thin-film substrate has a light-shielding function.
Also, in regard to the black matrix, it has been required to lower the reflectivity for easily seeing images by restraining the reflection images such as a face, etc., and the background onto a display panel as completely as possible and also to keep the optical density of the black matrix above a definite level because if the light from a back light in the inside of the panel transmits, the color tone does not become clear.
From the view point, to produce a low-reflective thin-film substrate having a low reflectivity and a definite optical density, a method of forming film(s) by sputtering a material containing chromium metal as a target has hitherto been known and utilized as a typical technique.
However, in general, chromium having other valences than hexavalence has less toxicity but chromium having a hexa-valence has a strong toxicity and there is a problem of causing an environmental pollution. Thus, recently, in view of public opinion, there is a tendency of restraining the use of chromium metal in the production of liquid crystal panels and a low-reflective thin-film substrate containing no chromium component has been required.
Furthermore, although in a known low-reflective chromium thin film, the minimum reflectivity is 0.5% or lower (the wavelength is about 600 nm) and the optical density is 4.0 or higher, it is the present situation that the average reflectivity (the value obtained by summing up the reflectivities per an interval of, for example, 1 nm in wavelength and dividing the sum up value by the number of the measured points) in a wavelength region of from 400 to 700 nm (almost the whole region of visible light) is 1.5% or higher and the maximum reflectivity exceeds 5%. The reflectivity is confirmed by measuring an aluminum thin film as a reference using a microspectroscope, OSP-SP 200, trade name, manufactured by Olympus Optical Company Limited and does no contain the reflectivity from a glass surface.
In general, in a low-reflective thin-film substrate wherein the minimum reflectivity is 0.5% or lower and the maximum reflectivity exceeds 5%, the reflected color is influenced by the wavelength showing the maximum reflectivity. In fact, for example, in the wavelength region of from 400 to 700 nm, when the wavelength showing the maximum reflectivity is in a short wavelength side of 400 nm (near), a bluish purple color is emphasized in the reflected color and when the wavelength showing the maximum reflectivity is in a long wavelength side of 700 nm (near) , a red color is emphasized in the reflected color.
When such a low-reflective thin-film substrate is used as a projector frame, there is a fault that the frame projected onto a screen becomes bluish purple or red.
Also, it is proposed to use a resin as a low-reflective thin-film substrate but in the case of using the resin, because the resin is inferior in the points of the light resistance and the heat resistance as compared with the case of using inorganic materials, there is a problem that the optical characteristics are greatly deteriorated by an intense light source.
Accordingly, recently, the realization of a low-reflective thin-film substrate which does not cause an environmental problem as caused in the case of a chromium substrate as described above as well as has a low reflectivity in almost all the wavelength region of visible light and also is excellent in the light resistance has been required.